Method and apparatus for performing work in a three dimensional space

Abstract

Method and apparatus for moving a workpiece and/or a tool to various locations in a three-dimensional space to perform operations on the workpiece wherein a micro-computer numeric control system is used to provide a multi-axis motion control system using DC electric servo motors, each of which responds to its own control system to operate mechanisms which cooperate to perform the desired operations on the workpiece.

What is claimed is: 
     
       1. A method for controlling the relative movement of a workpiece and a tool in a three dimensional space so as to perform desired operations on the workpiece comprising: providing a motor control means for moving at least one of said workpiece and tool in a direction along an x, y or z axis; and   generating a signal by concurrently performing a first set of tasks including foreground tasks, midground tasks and background tasks;   transmitting said signal to a motor control board;   generating another signal by said motor control board by concurrently performing a second set of tasks including foreground tasks, midground tasks and background tasks; and   using said another signal to operate said motor control means.   
     
     
       2. A method as in claim 1 and further comprising: executing said foreground tasks of said first set of tasks at periodic time intervals.   
     
     
       3. A method as in claim 2 and further comprising: generating a set of coordinates for said x axis and said y axis by said midground tasks of said first set of tasks; and   executing said generation of coordinates at periodic time intervals.   
     
     
       4. A method as in claim 3 wherein: said periodic time interval for said foreground tasks is about 1 millisecond; and   said periodic time interval for said generation of coordinates is about 10 milliseconds.   
     
     
       5. A method as in claim 3 wherein said set of coordinates is generated by: dividing a 360° circle into eight sectors so that the angle trim in radians is always a fraction less than 1;   executing said midground and background tasks during each of said time intervals.   
     
     
       6. A method as in claim 3 and further comprising: executing said foreground tasks of said second set of tasks at periodic time intervals.   
     
     
       7. A method as in claim 6 and further comprising: executing said midground and background tasks of said second set of tasks during said periodic time interval of said foreground tasks of said second set of tasks.   
     
     
       8. A method as in claim 7 wherein: said periodic time interval for said foreground tasks of said second set of tasks is about 200 microseconds.   
     
     
       9. A method as in claim 7 wherein said midground tasks include: controlling the velocity mode of each of said motor control means using pulse width modulation.   
     
     
       10. A method as in claim 9 wherein said controlling of said velocity mode of each of said motor control means comprises: calculating the PWM for said motor control means using the formula:   PWM=(Cv)×(Vc)+PWM.0.+(Cg)×(Vc-Va)        where:   PWM is the new pulse width required   Cv is the slope of the velocity gradient   Vc is the command velocity   PWM.0. is the PWM required to turn the motor   Cg is the velocity servo gain   Va is the actual velocity.   
     
     
       11. A method as in claim 9 wherein said controlling of said velocity mode of each of said motor control means when said motor is near a stop lock position comprises: calculating the PWM for said motor control means using the formula:   PWM=PWM.0.+(Cp)×(De)+(Cd)×(Va)        where:   PWM is the desired pulse width   PWM.0. is the PWM required to turn the motor   Cp is the position servo gain   De is the distance error   Cd is the coefficient of velocity damping   Va is the actual velocity.   
     
     
       12. A method as in claim 9 and further comprising: using a DC servo electric motor as said motor; and   operating said DC servo electric motor at a relatively high voltage.   
     
     
       13. A method as in claim 12 wherein: said relatively high voltage is about 160 volts.   
     
     
       14. A method as in claim 12 and further comprising: connecting a rotatable member to said motor so that rotation of said motor rotates said rotatable member;   connecting said workpiece to said rotatable member so that rotation of said rotatable member moves said workpiece; and   establishing a relatively high speed drive ratio between about 2.4 and 3.2 to 1 between said rotatable member and said DC servo electric motor.   
     
     
       15. A method as in claim 14 wherein: said ratio between about 3.2 to 1 is along said x and y axis; and   said ratio between about 2.4 to 1 is along said Z-axis.   
     
     
       16. A method as in claim 7 and further comprising: using a DC servo electric motor as said motor;   connecting a rotatable member to said motor so that rotation of said motor rotates said rotatable member;   connecting said workpiece to said rotatable member so that rotation of said motor rotates said rotatable member;   using the damping characteristics of said DC servo electric motor to hold said workpiece in a locked position.   
     
     
       17. A method as in claim 16 and further comprising: maintaining the electrical circuit for said DC servo electric motor closed so as to use said dampening characteristic of said DC servo electric motor.   
     
     
       18. A method as in claim 16 and further comprising: placing compensating inductors around at least four chokes so that either of two pairs provides the inductive compensation to maintain said electrical circuit closed.   
     
     
       19. A method as in claim 18 wherein said electrical circuit comprises: flowing current in two halves of a cycle through said electrical circuit;   flowing current in the first half of the cycle from a high voltage direct current source, through a power transistor, said DC servo electric motor in a positive direction, a choke, a power transistor and back to said high voltage direct circuit source; and   flowing current in the second half of the cycle from said high voltage direct current source, through a power transistor, said DC servo electric motor in a negative direction, a choke, a power transistor and back to said high voltage direct current source.   
     
     
       20. A method as in claim 19 and further comprising: controlling the inductance in said electric circuit to about 15 mH.   
     
     
       21. A method as in claim 19 and further comprising: generating a signal to be fed to said electric circuit for controlling the movement of said DC servo electric motor;   processing said signal by an opto-isolator chip; and   feeding said signal to said DC servo electric motor.   
     
     
       22. In apparatus for use in moving a movable element in a computer controlled mechanism wherein the movable element is connected to a rotatable member so that rotation of the rotatable member moves the movable element and wherein the rotatable member is rotated by a DC servo electric motor, the improvement comprising: means for establishing a relatively high speed drive ratio of between about 2.4 and 3.2 to 1 between said rotatable member and said DC servo electric motor.   
     
     
       23. The improvement as in claim 22 wherein: said DC servo electric motor operates at a relatively high DC voltage.   
     
     
       24. The improvement as in claim 23 wherein: said relatively high DC voltage is about 160 volts.   
     
     
       25. The improvement as in claim 24 wherein said means for establishing a relatively high drive ratio includes: a belt drive means.   
     
     
       26. The improvement as in claim 25 wherein said belt drive means comprises: a first pulley secured to the free end of the shaft of said DC servo electric motor;   a plurality of spaced apart teeth on the periphery of said first pulley;   a second pulley secured to the free end of said rotatable member;   a plurality of spaced apart teeth on the periphery of said second pulley;   said second pulley having a diameter greater than the diameter of said first pulley;   a continuous cog belt having a plurality of spaced apart cogs on the inner surface thereof; and   said continuous cog belt being trained around said first and second pulleys so that said cogs mesh with said plurality of teeth on said first and second pulleys so as to provide a positive drive between said DC servo electric motor and said rotatable member.   
     
     
       27. The improvement as in claim 22 wherein: said DC servo electric motor is controlled solely by an optical encoder.   
     
     
       28. The improvement as in claim 27 wherein: said optical encoder utilizes a disk having about 500 lines per revolution.   
     
     
       29. The improvement as in claim 28 wherein said optical encoder includes: a transparent disk having a plurality of radially extending lines thereon;   a first light emitting diode positioned adjacent to one side of said disk and opposite to said plurality of lines; and   a first photo transistor positioned adjacent to the other side of said disk and opposite to said plurality of lines so that light emitted by said first light emitting diode may pass through an area between adjacent lines and be picked up by said first photo transistor.   
     
     
       30. The improvement as in claim 29 and further comprising: a second light emitting diode positioned to said one side of said metal disk and opposite to said plurality of lines;   a second photo transistor positioned adjacent to said other side of said disk and opposite to said plurality of lines so that light emitted by said second light emitting diode may pass through an area between adjacent lines and be picked up by said second photo transistor; and   said second light emitting diode and said second photo transistor are spaced 90° from said first light emitting diode and said first photo transistor.   
     
     
       31. Apparatus for controlling the relative movement of a workpiece and a tool in a three-dimensional space so as to perform desired operations on the workpiece comprising: means for mounting a workpiece on a work table;   means for mounting a tool adjacent to said work table;   means for causing relative movement of one of said workpiece and said tool in a three-dimensional space along a x-axis, a y-axis or a z-axis;   said means for causing relative movement includes a DC servo electric motor associated with each of said x-axis, y-axis and z-axis;   a motor control board for each of said DC servo electric motors;   each of said motor control boards concurrently performing a set of tasks including foreground tasks, midground tasks and background tasks to generate a signal; and   means for transmitting each generated signal to an associated one of said DC servo electric motors.   
     
     
       32. Apparatus for controlling the relative movement of a workpiece and a tool in a three dimensional space so as to perform desired operations on said workpiece comprising: means for mounting a workpiece on a work table;   means for mounting a tool adjacent to said work table;   means for causing relative movement of one of said workpiece and said tool in a three-dimensional space along a x-axis, a y-axis or a z-axis;   said means for causing relative movement includes a DC servo electric motor associated with each of said x-axis, y-axis and z-axis;   a motor control board for each of said DC servo electric motors;   each of said motor control boards concurrently performing a set of tasks to generate a signal;   means for transmitting each generated signal to an associated one of said DC servo electric motors; and   an opto-isolator chip located between each of said motor control boards and each of said DC servo electric motors and through which said signal is transmitted.   
     
     
       33. Apparatus as in claim 31 and further comprising: an electric circuit for using the damping characteristics of each of said DC servo electric motors to retain said means for causing relative movement in a stop hold mode.   
     
     
       34. Apparatus as in claim 33 wherein: said electric circuit includes at least four chokes.   
     
     
       35. Apparatus as in claim 34 and further comprising: an H style motor drive amplifier for each of said DC servo electric motors; and   one of said chokes being located in each leg of said H style motor drive amplifiers.   
     
     
       36. Apparatus as in claim 35 wherein said electric circuit comprises: a 160 volt DC power source, a power transistor, a choke, a DC servo electric motor positive direction, another choke and another power transistor in a first half cycle; and   a 160 volt DC power source, a power transistor, a choke, a DC servo electric motor negative direction, another choke and another power transistor in a second half-cycle.   
     
     
       37. Apparatus as in claim 31 wherein: said signal is generated in accordance with the following formula:   PWM=(Cv)×(Vc)+PWM.0.+(Cg)×(Vc-Va)        where:   PWM is the new pulse width desired   Cv is the slope of the velocity   Vc is the commanded velocity   PWM.0. is the PWM required to turn the motor   Cg is the velocity servo gain   Va is the actual velocity.   
     
     
       38. Apparatus as in claim 31 wherein: said signal is generated in accordance with the following formula when said motor is near a stop lock position:   PWM=PWM.0.+(Cp)×(De)+(Cd)×(Va)        where:   PWM is the desired pulse width   PWM.0. is the PWM required to turn the motor   Cp is the position servo gain   De is the distance error   Cd is the coefficient of velocity damping   Va is the actual velocity.   
     
     
       39. Apparatus as in claim 31 wherein said means for causing movement comprises: a rotatable member for each of said x-axis, y-axis and z-axis; and   means for connecting each of said rotatable members to one of said DC servo electric motors so that the ratio of rotation of said rotatable member to said DC servo electric motor is at least about 2.4 to 1.   
     
     
       40. Apparatus as in claim 31 wherein said means for causing movement comprises: a rotatable member for each of said x-axis and said y-axis; and   means for connecting each of said rotatable members to one of said DC servo electric motors so that the ratio of rotation of said rotatable member to said DC servo electric motor is at least 3.2 to 1.   
     
     
       41. Apparatus as in claim 31 and further comprising: an optical tachometer associated with each of said DC servo electric motors; and   each of said optical tachometers having about 500 lines per revolution.   
     
     
       42. Apparatus as in claim 41 and further comprising: an optical encoder associated with each one of said optical tachometer.   
     
     
       43. Apparatus as in claim 31 and further comprising: means for generating a signal by concurrently performing a first set of tasks including foreground tasks, midground tasks and background tasks and transmitting said signal to each of said motor control boards.